Conventionally, radiographic imaging machines that perform radiographic imaging for the purpose of medical diagnosis have been known. An example of this type of radiographic imaging machine is a mammography machine that images the breasts of an examinee for the purpose of early detection of breast cancer. Furthermore, in connection with mammography machines, technologies that perform tomosynthesis imaging, in which radiation is applied at different angles to the breast of an examinee to image the breast, are known. In tomosynthesis imaging, tomographic images (substantially) parallel to the detection plane are generated at a predetermined slice width by reconstructing them from plural radiographic images (hereinafter called projection images) that have been captured by applying radiation to a subject while changing the angle of incidence of the radiation with respect to the detection plane.
However, in tomosynthesis imaging, the angles when applying the radiation are restricted, so even if the tomographic images are reconstructed by simply superimposing the projection images using the back-projection method, for example, sometimes a phantom image of an object ends up appearing in a region where that object is not really present. More specifically, sometimes, due to back-projection, a phantom image ends up appearing in a region where an object is not really present in a tomographic image at a slice position differing from a tomographic image at a slice position where the object is present. If the phantom image is too conspicuous, it becomes difficult to ascertain the object of interest. The same situation also occurs when using other methods to implement tomographic image reconstruction.
The filtered back-projection (FBP) method, which is a representative CT reconstruction method, can also be applied to reconstruct tomographic images by back-projecting them from projection images on which filtering has been uniformly performed. This can mitigate phantom images in the depth direction to a certain extent, but in the case of tomosynthesis imaging, if filtering is uniformly performed, sometimes the density of the subject image in the tomographic images ends up being quite different from what it is in the projection images.
On the other hand, in CT imaging, which compared to tomosynthesis imaging has no restrictions on the angles at which the radiation is applied, when tomographic images have been reconstructed using the FBP method that performs uniform filtering on each of the projection images and performs back-projection, the phantom images can be cancelled out when the projection images are superimposed on top of one another during back-projection, and phantom images (artifacts) on the tomographic images that are reconstructed are controlled. Consequently, the situation described above is a problem unique to tomosynthesis imaging.
As a technology for controlling artifacts in tomosynthesis imaging, a method comprising identifying a plurality of non-uniform weighting factors for use in back-projection processing and back-projecting image data by application of the non-uniform weighting factors is known (e.g., see JP-A No. 2005-152658). Furthermore, although it does not involve tomosynthesis imaging, an image processing device that performs image processing on the basis of the angle of incidence of radiation as correction processing with respect to a radiographic image obtained by ordinary two-dimensional imaging (ordinary imaging in which the radiation is applied to the subject from a fixed position without moving the radiation source) is also known (e.g., see JP-A No. 2005-7061).